1. Field of Use
This invention relates generally to a control system for hydraulically controlled components in the power train between the engine and the drive wheels of a motor grader. More specifically, the invention relates to a fluid logic control system for operating a main engine clutch, a high-low range transmission and a multispeed main transmission in the drive train in a predetermined sequence in response to actuation of a speed range control valve to provide an increased number of possible speed ranges and improved transition between speed ranges.
2. Description of the Prior Art
In order to provide a desired number of speed ranges for the output shaft of a power train it was fromerly the practice either to employ a single transmission designed to provide the necessary number of speed ranges or to employ a low speed-high speed range transmission in combination with a multispeed main transmission and controls for operating the two transmissions in a sequence which provided the desired number of shift ranges. Some prior art control means required the operator to actuate separate controls to operate the two transmissions and the main engine clutch, but such arrangements were mechanically complex and required a high degree of operator skill and attention to achieve smooth and efficient shifting. Other prior art control means designed to operate the two transmissions in a predetermined sequence relied on mechanical arrangements which were not wholly dependable, required repeated adjustment and were not fully automatic but required additional operator input to carry out a proper shifting sequence.